Delay-Tolerant Networking Working Group S. Burleigh
Internet Draft JPL, Calif. Inst. Of Technology
Intended status: Standards Track January 31, 2019
Expires: August 2019
Bundle-in-Bundle Encapsulation
draft-ietf-dtn-bibect-01.txt
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Abstract
This document describes Bundle-in-Bundle Encapsulation (BIBE), a
Delay-Tolerant Networking (DTN) Bundle Protocol (BP) "convergence
layer" protocol that tunnels BP "bundles" through encapsulating
bundles. The services provided by the BIBE convergence-layer
protocol adapter encapsulate an outbound BP "bundle" in a BIBE
convergence-layer protocol data unit for transmission as the payload
of a bundle. Security measures applied to the encapsulating bundle
may augment those applied to the encapsulated bundle. The protocol
includes a mechanism for recovery from loss of an encapsulating
bundle, called "custody transfer". This mechanism is adapted from
the custody transfer procedures described in the experimental Bundle
Protocol specification developed by the Delay-Tolerant Networking
Research group of the Internet Research Task Force and documented in
RFC 5050.
Table of Contents
1. Introduction...................................................2
2. Conventions used in this document..............................4
3. BIBE Design Elements...........................................4
3.1. BIBE Endpoints............................................4
3.2. BIBE Protocol Data Units..................................4
3.3. Custody Signals...........................................6
3.4. Custody Transfer Status Reports...........................7
4. BIBE Procedures................................................8
4.1. BPDU Transmission.........................................8
4.2. BPDU Reception............................................8
4.3. Retransmission Timer Expiration..........................10
4.4. Custody Signal Reception.................................10
5. Security Considerations.......................................11
6. IANA Considerations...........................................11
7. References....................................................11
7.1. Normative References.....................................11
7.2. Informative References...................................11
8. Acknowledgments...............................................11
Appendix A. For More Information.................................13
Appendix B. CDDL expression......................................14
1. Introduction
This document describes Bundle-in-Bundle Encapsulation (BIBE), a
Delay-Tolerant Networking (DTN) Bundle Protocol (BP) [RFC5050]
"convergence layer" protocol that tunnels BP "bundles" through
encapsulating bundles.
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Conformance to the bundle-in-bundle encapsulation (BIBE)
specification is OPTIONAL for BP nodes. Each BP node that conforms
to the BIBE specification provides a BIBE convergence-layer adapter
(CLA) that is implemented within the administrative element of the
BP node's application agent. Like any convergence-layer adapter,
the BIBE CLA provides:
. A transmission service that sends an outbound bundle (from the
bundle protocol agent) to a peer CLA. In the case of BIBE, the
sending CLA and receiving peer CLA are both BP nodes.
. A reception service that delivers to the bundle protocol agent
an inbound bundle that was sent by a peer CLA (itself a BP
node) via the BIBE convergence layer protocol.
The BIBE CLA performs these services by:
. Encapsulating outbound bundles in BIBE protocol data units,
which take the form of Bundle Protocol administrative records
as described later.
. Requesting that the bundle protocol agent transmit bundles
whose payloads are BIBE protocol data units.
. Taking delivery of BIBE protocol data units that are the
payloads of bundles received by the bundle protocol agent.
. Delivering to the bundle protocol agent the bundles that are
encapsulated in delivered BIBE protocol data units.
Bundle-in-bundle encapsulation may have broad utility, but the
principal motivating use case is the deployment of "cross domain
solutions" in secure communications. Under some circumstances a
bundle may arrive at a node that is on the frontier of a sector of
network topology in which augmented security is required, from which
the bundle must egress at some other designated node. In that case,
the bundle may be encapsulated within a bundle to which the
requisite additional BP Security (BPSEC) [bpsec] extension block(s)
can be attached, whose source is the point of entry into the
insecure region (the "security source") and whose destination is the
point of egress from the insecure region (the "security
destination").
Note that:
. If the payload of the encapsulating bundle is protected by a
Bundle Confidentiality Block (BCB), then the source and
destination of the encapsulated bundle are encrypted, providing
defense against traffic analysis that BPSEC alone cannot offer.
. Bundles whose payloads are BIBE protocol data units may
themselves be forwarded via a BIBE convergence-layer adapter,
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enabling nested bundle encapsulation to arbitrary depth as
required by security policy.
. Moreover, in the event that no single point of egress from an
insecure region of network topology can be determined at the
moment a bundle is to be encapsulated, multiple copies of the
bundle may be encapsulated individually and forwarded to all
candidate points of egress.
The protocol includes a mechanism for recovery from loss of an
encapsulating bundle, called "custody transfer". This mechanism is
adapted from the custody transfer procedures described in the
experimental Bundle Protocol specification developed by the Delay-
Tolerant Networking Research group of the Internet Research Task
Force and documented in RFC 5050. Custody transfer is a convention
by which the loss or corruption of BIBE encapsulating bundles can be
mitigated by the exchange of other bundles, which are termed
"custody signals".
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
3. BIBE Design Elements
3.1. BIBE Endpoints
BIBE convergence-layer protocol endpoints, also known as BIBE
convergence-layer adapters (BCLAs), are the Administrative Elements
of Bundle Protocol nodes that conform to the BIBE protocol
specification. The node of which a given BCLA is one component is
termed the BCLA's "local node".
3.2. BIBE Protocol Data Units
Notionally, a BCLA is assumed to implement in some way, for each
neighboring node to which the local node issues BIBE Protocol Data
Units (BPDUs), the following two data resources:
1. A "custodial transmission count" (CTC). A CTC is a
monotonically increasing integer indicating the number of
"custodial" BPDUs - that is, BPDUs for which custody transfer
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was requested - that have been issued to the neighboring node
by the local node since instantiation of the local node.
2. A "custodial transmission database" (CTDB), a notional array of
"custodial transmission items" (CTIs). The CTDB contains one
CTI for each custodial BPDU issued to the neighboring node, by
the local node, for which (a) no custody disposition has yet
been received in any custody signal (as discussed later) and
(b) the bundle encapsulated in that BPDU has not yet been
destroyed due to, e.g., time-to-live expiration. Each CTI
notionally contains:
a. A reference to the bundle encapsulated in the
corresponding BPDU.
b. The "transmission ID" of the corresponding BPDU, as
discussed below.
c. A "retransmission time" indicating the time by which
custody disposition for the corresponding BDPU is
expected.
A BIBE protocol data unit is a Bundle Protocol administrative record
whose record type code is 3 (i.e., bit pattern 0011), constructed as
follows.
Each BPDU SHALL be represented as a CBOR array. The number of
elements in the array SHALL be 3.
The first item of the BPDU array SHALL be the "transmission ID" for
the BPDU, represented as a CBOR unsigned integer. The transmission
ID for a BPDU for which custody transfer is NOT requested SHALL be
zero. The transmission ID for a BPDU for which custody transfer IS
requested SHALL be the current value of the local node's custodial
transmission count, plus 1.
The second item of the BPDU array SHALL be the BPDU's retransmission
time (i.e., the time by which custody disposition for this BPDU is
expected), represented as a CBOR unsigned integer. Retransmission
time for a BPDU for which custody transfer is NOT requested SHALL be
zero. Retransmission time for a BPDU for which custody transfer IS
requested SHALL take the form of a "DTN Time" as defined in the
Bundle Protocol specification; determination of the value of
retransmission time is an implementation matter that is beyond the
scope of this specification and may be dynamically responsive to
changes in connectivity.
The third item of the BPDU array SHALL be a single BP bundle, termed
the "encapsulated bundle", represented as a CBOR byte string of
definite length.
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3.3. Custody Signals
A "custody signal" is a Bundle Protocol administrative record whose
record type code is 4 (i.e., bit pattern 0100) and whose content is
constructed as follows.
The content of each custody signal SHALL be represented as a CBOR
array. The number of elements in the array SHALL be 2.
The first item of the custody signal content array SHALL be a
disposition code represented as a CBOR unsigned integer. Valid
disposition codes are defined as follows:
+---------+--------------------------------------------+
| Value | Meaning |
+=========+============================================+
| 0 | Custody accepted. |
+---------+--------------------------------------------+
| 1 | No further information. |
+---------+--------------------------------------------+
| 2 | Reserved for future use. |
+---------+--------------------------------------------+
| 3 | Redundant (reception by a node that |
| | already has a copy of this bundle). |
+---------+--------------------------------------------+
| 4 | Depleted storage. |
+---------+--------------------------------------------+
| 5 | Destination endpoint ID unintelligible. |
+---------+--------------------------------------------+
| 6 | No known route destination from here. |
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+---------+--------------------------------------------+
| 7 | No timely contact with next node on route. |
+---------+--------------------------------------------+
| 8 | Block unintelligible. |
+---------+--------------------------------------------+
| (other) | Reserved for future use. |
+---------+--------------------------------------------+
Figure 1: Disposition Codes
The second item of the custody signal content array SHALL be a
"disposition scope report", represented as a CBOR indefinite-length
array. Each item of the disposition scope report array SHALL be a
"disposition scope sequence", represented as a CBOR array of two
elements. The first element of each disposition scope sequence
array SHALL be the first transmission ID in a sequence of 1 or more
consecutive transmission IDs corresponding to BPDUs to which the
custody signal's disposition is declared to apply; the second
element of each disposition scope sequence array SHALL be the number
of transmission IDs in that sequence. Both are represented as CBOR
unsigned integers.
A custody signal constitutes an assertion by the source of that
administrative bundle that the indicated disposition code applies to
all BPDUs identified by the transmission IDs enumerated in the
custody signal's disposition scope report. If the disposition code
is zero, then the source of the custody signal has accepted custody
of all bundles that were encapsulated in the indicated BPDUs.
Otherwise the source of the custody signal has refused custody of
all bundles that were encapsulated in the indicated BPDUs, for the
indicated reason.
3.4. Custody Transfer Status Reports
A "custody transfer status report" is a bundle status report with
the "reporting node attempted custody transfer" flag set to 1.
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4. BIBE Procedures
4.1. BPDU Transmission
When a BCLA is requested by the bundle protocol agent to send a
bundle to the peer BCLA(s) included in the BP endpoint identified by
a specified BP endpoint ID:
. The BCLA SHALL generate, as defined in Section 6.2 of the
Bundle Protocol specification (a work in progress), a BPDU for
which the third element of the content array is the bundle that
is to be transmitted. The destination of the bundle whose
payload is the BPDU (termed the "encapsulating bundle") SHALL
be the specified BP endpoint. Selection of the values of the
parameters governing the forwarding of the encapsulating
bundle, other than the destination endpoint ID, is an
implementation matter. The parameter values governing the
forwarding of the BPDU's encapsulated bundle MAY be consulted
for this purpose.
. Note that any transmission request presented to a BCLA MAY
request that the transmission be subject to Custody Transfer,
provided that the destination EID of the request identifies a
singleton endpoint.
. If Custody Transfer is requested:
o The first element of the BPDU's content array MUST be the
BPDU's transmission ID, which SHALL be 1 more than the
current value of the BCLA's CTC for the node that is the
sole occupant of the BPDU's destination endpoint.
o The second element of the BPDU's content array MUST be the
BPDU's retransmission time as discussed in 3.2 above.
o The bundle protocol agent MUST add the retention constraint
"Custody accepted" to the encapsulated bundle.
o The BCLA MAY establish a retransmission timer for the
encapsulated bundle. If a retransmission timer is
established, it MUST be set to expire at the BPDU's
retransmission time.
. Otherwise, the first two elements of the BPDU's content array
MUST both be zero.
Note that the custody transfer retransmission timer mechanism
provides a means of recovering from loss of an encapsulating bundle
as indicated by non-arrival of a responding custody signal.
4.2. BPDU Reception
When a BCLA receives a BPDU from the bundle protocol agent (that is,
upon delivery of the payload of an encapsulating bundle):
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. If Custody Transfer was requested for this BPDU (as indicated
by a non-zero value of transmission ID):
o If the encapsulated bundle has the same source node ID,
creation timestamp, and (if that bundle is a fragment)
fragment offset and payload length as another bundle that
is currently retained at the BCLA's local node, then
custody transfer redundancy MUST be handled as follows:
. The BCLA SHALL add the BPDU's transmission ID to the
disposition scope report of a pending outbound
custody signal, destined for the node that was the
source of the encapsulating bundle, whose disposition
is the reason code from Figure 1 for "Redundant
reception".
o Otherwise, if the BCLA determines that its local node can
neither deliver nor forward the encapsulated bundle for
any of the reasons listed in Figure 1, then custody
transfer has failed. Custody transfer failure SHALL be
handled as follows:
. The BCLA SHALL add the BPDU's transmission ID to the
disposition scope report of a pending outbound
custody signal, destined for the node that was the
source of the encapsulating bundle, whose disposition
is the reason code from Figure 2 that indicates the
reason for the custody transfer failure.
o Otherwise, custody transfer has succeeded:
. The BCLA SHALL add the BPDU's transmission ID to the
disposition scope report of a pending outbound
custody signal, destined for the node that was the
source of the encapsulating bundle, whose disposition
is zero (indicating that custody was accepted).
o In each of these three cases:
. The pending outbound custody signal MAY then be
issued immediately, but alternatively it MAY be
issued at some time in the future, possibly enabling
additional BPDUs' transmission IDs to be added to the
same disposition scope report.
. If the "request reporting of custody transfer
attempted" flag in the encapsulating bundle's status
report request field is set to 1, and status
reporting is enabled, a custody transfer status
report whose reason code is the same as the pending
outbound custody signal's disposition SHOULD be
generated, destined for the report-to endpoint of the
encapsulating bundle.
. If Custody Transfer was NOT requested for this BPDU, or if
Custody Transfer was requested for this BPDU and custody
transfer succeeded, then the encapsulated bundle SHALL be
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delivered from the convergence layer adapter to the bundle
protocol agent, whereupon bundle reception SHALL be performed
as defined in section 5.6 of the Bundle Protocol specification
(a work in progress) as usual: the encapsulated bundle may be
forwarded, delivered, etc.
Note that the manner in which pending outbound custody signals are
managed, disposition scope reports are aggregated, and custody
signal transmission is initiated is an implementation matter that
is beyond the scope of this specification. Note, however, that
failure to deliver a custody signal prior to the earliest value of
retransmission time among all BPDUs enumerated in the custody
signal's disposition scope report may result in unnecessary
retransmission of one or more BPDUs.
4.3. Retransmission Timer Expiration
Upon expiration of a retransmission timer, the BCLA SHOULD remove
the corresponding CTI from the CTDB (destroying the associated
retransmission timer, if any) and notify the bundle protocol agent
that custodial transmission of the indicated bundle failed. This
notification may cause the indicated bundle to be re-forwarded
(possibly on a different route).
4.4. Custody Signal Reception
When a BCLA receives a custody signal from the bundle protocol agent
(that is, upon delivery of the payload of a custody-signal-bearing
bundle):
. If the custody signal's disposition is 0 (custody acceptance),
then for each transmission ID in the custody signal's
disposition scope report:
o The bundle protocol agent MUST remove the retention
constraint "Custody accepted" on the bundle referenced by
the corresponding CTI.
o The corresponding CTI MUST be removed from the CTDB
(destroying the associated retransmission timer, if any).
. Otherwise (custody refusal), for each transmission ID in the
custody signal's disposition scope report:
o The corresponding CTI MUST be removed from the CTDB
(destroying the associated retransmission timer, if any).
o Any further action taken by the BCLA is implementation-
specific and may depend on the reason code cited for the
refusal. For example, if the custody signal's reason code
was "Depleted storage", the BCLA might choose to notify
the bundle protocol agent that custodial transmission of
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the indicated bundle failed. If the reason code was
"Redundant reception", on the other hand, this might cause
the BCLA simply to instruct the bundle protocol agent to
remove the retention constraint "Custody accepted" on the
bundle referenced by the corresponding CTI and to revise
its algorithm for computing retransmission time.
5. Security Considerations
An adversary on a DTN-based network that can delete bundles could
delete a BIBE custody signal in transit. This could result in
unnecessary custodial retransmission, degrading network performance.
Alternatively, an adversary on a DTN-based network that can reorder
bundles could cause bundles to be delivered to a BCLA in an order
that complicates the efficient construction of disposition scope
reports in pending outbound custody signals. This could result in
inefficient custody transfer communications, again degrading network
performance.
Custody transfer in BIBE may be contraindicated in environments
characterized by such attacks.
6. IANA Considerations
The BIBE specification requires IANA registration of the new BIBE
administrative records (type codes 3 and 4) defined above.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
7.2. Informative References
[RFC5050] Scott, K. and S. Burleigh, "Bundle Protocol
Specification", RFC 5050, November 2007.
8. Acknowledgments
This work is freely adapted from [RFC5050], which was an effort of
the Delay Tolerant Networking Research Group. The following DTNRG
participants contributed significant technical material and/or
inputs to that document: Dr. Vinton Cerf of Google, Scott Burleigh,
Adrian Hooke, and Leigh Torgerson of the Jet Propulsion Laboratory,
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Michael Demmer of the University of California at Berkeley, Robert
Durst, Keith Scott, and Susan Symington of The MITRE Corporation,
Kevin Fall of Carnegie Mellon University, Stephen Farrell of Trinity
College Dublin, Peter Lovell and Howard Weiss of SPARTA, Inc., and
Manikantan Ramadas of Ohio University.
The custody transfer procedures defined in this specification are
adapted from the Aggregate Custody Signals draft specification
authored in 2010-2012 by Sebastian Kuzminsky and Andrew Jenkins,
then of the University of Colorado at Boulder.
Although the BIBE specification diverges in some ways from the
original Bundle-in-Bundle Encapsulation Internet Draft authored by
Susan Symington, Bob Durst, and Keith Scott of The MITRE Corporation
(draft-irtf-dtnrg-bundle-encapsulation-06, 2009), the influence of
that earlier document is gratefully acknowledged.
This document was prepared using 2-Word-v2.0.template.dot.
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Appendix A. For More Information
Please refer comments to dtn@ietf.org. The Delay Tolerant Networking
Research Group (DTNRG) Web site is located at http://www.dtnrg.org.
Copyright (c) 2019 IETF Trust and the persons identified as authors
of the code. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, is permitted pursuant to, and subject to the license
terms contained in, the Simplified BSD License set forth in Section
4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info).
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Appendix B. CDDL expression
For informational purposes, Carsten Bormann has kindly provided an
expression of the Bundle Protocol specification in the CBOR Data
Definition Language (CDDL). Portions of CDDL expression that bear
on the custody transfer extension are presented below, somewhat
edited by the authors. Note that wherever the CDDL expression is in
disagreement with the textual representation of the BP specification
presented in the earlier sections of this document, the textual
representation rules.
admin-record-choice /= BIBE-PDU
BIBE-PDU = [3, [transmission-ID: uint,
retransmission-time: uint,
encapsulated-bundle: bytes,
admin-common]]
admin-record-choice /= custody-signal
custody-signal = [4, [disposition-code: uint,
disposition-scope-report,
admin-common]]
disposition-scope-report = *disposition-scope-sequence
disposition-scope-sequence = [first-transmission-ID: uint,
number-of-transmission-IDs: uint]
Authors' Address
Scott Burleigh
Jet Propulsion Laboratory, California Institute of Technology
4800 Oak Grove Dr.
Pasadena, CA 91109-8099
US
Phone: +1 818 393 3353
Email: Scott.Burleigh@jpl.nasa.gov
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